1. Technical Field
The present invention relates to a transmission device and method for transmitting an audio signal through a video signal line. In particular, the present invention relates to a transmission device and method using red (R), green (G), and blue (B) video signal lines of a video graphics array (VGA) in a computer having a VGA color monitor.
2. Background Art
Generally, a monitor is a peripheral device which processes information data received from an information data system such as a computer system and provides a visual display of processed information data on a screen. Such a monitor is typically available in either black and white known as monochrome monitor or high resolution color known as color graphics adapter (CGA), video graphics adapter (VGA) and enhanced graphics adapter VEGA) monitor. Monochrome, CGA, EGA monitors provide a visual display of graphics data by processing digital signals. VGA monitors, by contrast, provide a visual display of graphics data by processing analog signals. The information data received from a computer system for a visual display comes in two different types of signals, a video signal format and an audio signal format. There are known signal transmission techniques for a broadcasting station in which an audio signal is transmitted during a non-video portion of a video signal such as disclosed, for example, in U.S. Pat. No. 3,423,520 for Time Division Multiplexing Of Audio And Video Signals issued to Kelly, U.S. Pat. No. 3,902,007 for Audio And Video Plural Source Time Division Multiplex For An Educational TV System issued to Justice, U.S. Pat. No. 4,983,967 for Transmission Of Audio In A Video Signal issued to McKenzie, U.S. Pat. No. 5,150,211 for Method And System For Multiplexing Audio And Video Signals To Distribute Still Pictures With Accompanying Sound issued to Charbonnel et al., and U.S. Pat. No. 5,351,090 for Video And Audio Signal Multiplexing Apparatus And Separating Apparatus issued to Nakamura. None however relates to the cable transmission of audio and video signals between a computer system and a monitor for audio and video production.
In a conventional computer system, the video signal is typically transmitted to a monitor in accordance with horizontal and vertical synchronization signals for a visual display. The audio signal which is output from a sound card or a CD-ROM (compact disk read only memory) mounted in the computer system, on the other hand, is transmitted not to the monitor but through an audio signal processing unit mounted internally or externally to the computer system through a separate audio cable. That is, the conventional transmission of an audio signal and a video signal in a computer system requires two separate transmission cables for audio and video generation on a monitor.